1. Field of the Invention
The invention concerns a magnetic resonance antenna and a method.
2. Description of the Prior Art
Modern magnetic resonance systems normally operate with multiple different antennas (also called coils in the following) to emit radio-frequency pulses for nuclear magnetic resonance excitation and/or to receive the induced magnetic resonance signals. A magnetic resonance system typically has a larger whole-body coil (also called a body coil or BC) that is normally permanently installed in the apparatus, as well as multiple small local coils (also called surface coils or LCs). In contrast to the whole-body coil, the local coils serve acquire detailed images of body parts or organs of a patient that are located relatively close to the body surface. For thus purpose the local coils are applied directly at the point of the patient at which the region to be examined is located. In the use of such a local coil, in many cases transmission is done with the whole-body coil (as a transmission coil) permanently installed in the magnetic resonance system, and the induced magnetic resonance signals are received with the local coil (as a reception coil). So that the coils cannot interact with one another, the reception coil is detuned in the transmission phase and the transmission coil is detuned in the reception phase. In detuning, the resonant frequency of the respective antenna is shifted.
Multiple magnetic resonance antennas that have a configuration known as a birdcage structure are used as a whole-body coil. Such an antenna has a number of longitudinal antenna rods arranged as a cylinder and running parallel to each other, these longitudinal antenna rods being connected (in terms of radio frequency) among one another at the ends by antenna ferrules. The longitudinal antenna rods and antenna ferrules can in principle be fashioned in an arbitrary form. In many cases, they are conductor traces that are applied on a flexible conductor trace film, the conductor traces are wound in the shape of a cylinder around the measurement space (examination volume) in which the examination subject is located during the examination. In a whole-body coil, the birdcage structure surrounds the patient receptacle space in which the patient is supported during the measurement. For local coils in the form of a birdcage structure, the measurement space serves to accommodate the head or other extremities of a patient in order to examine this region precisely.
In principle there are various possibilities to detune such magnetic resonance antennas with a birdcage structure.